| DETAILED USERS INSTRUCTIONS |
| The gauge has two parts. The first part is a worksheet, that simulates a template that the navigator uses to work the details of each sextant shot. Before the shot he enters the data on the first four rows, and the sextant shot results are automatically transcribed to the third row. The bottom row displays the magnetic variation at the aircraft's current location, and the GMT in the game. The second part of the gauge is a business end view of the sextant itself, with four functioning knobs which will be described below, and an enlarged eyepiece that pops up to show the star and the bubble during the shot itself (when the navigator would have his eye pressed against the eyepiece). 1. Worksheet |
| To enter the assumed latitude of the user at the time of the shot there are four hot-buttons as shown in the figure to the left. The white boxes represent the locations of the buttons. For the degrees entry, the hot-button to its left decreases the latitude by 2 degrees, and the right button increases it by 2 degrees. For the minutes, the left button decreases the latitude by 5 minutes, and the right button increases it. The tooltip will show a + or a - when you are on the button. You must round off to the nearest 5 minutes of latitude. South latitudes are negative numbers. |
| figure 11 To enter the assumed longitude, there are identical hot-buttons on the second row. West longitudes are entered as negative numbers e.g. W80 degrees is -80 degrees. |
| To enter the assumed star azimuth from the assumed position at the time of the shot there are four hot-buttons, as shown in the figure to the left. The innermost two boxes change the azimuth by one degree, and the outer boxes change the azimuth by 10 degrees. Increases are on the right. The azimuth is generally entered as positive degrees east of north. Negative azimuth is interpreted as degrees west of north. |
| figure 12 2. Sextant |
| For the assumed elevation of the star, since the real sextant operation calls for entering this value into the sextant, you do the same. The elevation cannot be negative. It is entered as a coarse elevation, in 2 degree steps, and a fine elevation, in 5 minute steps. See the figure below for the location of these two knobs. Clicking on the top half of the knob increases the elevation, and the lower half decreases it. |
| figure 13 To start the one minute average once the assumed positions are entered, there is a hot-button on the sextant where the eyepiece is. |
| Hovering the mouse on the eyepiece will give you the view as shown in the figure to the left. The tooltip prompts you with what will happen when you click the hot-button. Clicking on it steps it through the 1. Start, get a one minute average and display the results, and 2. Reset. You don't have to wait the full minute for an average, but may click the light again to advance and display the results. |
| figure 14 Don't forget to reset it before you attempt to start a new "star shot". You have to enter the Latitude and Longitude to the nearest 5 minutes of arc. This was done to speed up the process of setting up the worksheet, and the expected ease of finding the 5 minute lines on your plotting chart. The figure below shows a typical night sextant shot being prepared. When you start the gauge for the first time in any flight, there will be no bubble displayed. This is consistent with real Mark IX operating instructions, which call for removing the bubble before storage. To "make" a bubble, you use the bubble control wheel. You have a choice of three bubble sizes. See the figure below to locate the bubble control wheel, and the tool tip that indicates the size of the bubble. A "made" bubble may be used day or night. You may change the bubble size at any time. Note that the setting of the elevation drives both the star assumed elevation row, and the sextant elevation row. Clicking near the top of the fine elevation knob raises the position of the star in the display, by lowering the elevation angle of the "mirror" that controls the measured angle. In this particular figure below, there is no star (Sun) showing. This is what the sextant shows when your assumed position is more than about 350 NM from your actual position, and a useful shot cannot be made. Clicking the hot-button on the eyepiece again will reset the sextant so that you may guess again (re-estimate) what your position is. As you can see, the assumed longitude is -86 degrees, while the aircraft is as -76 degrees longitude. If you were in range the star would show up, and you should slowly adjust the fine elevation knob to move the mirror angle up or down so that the star appears centered inside the bubble. Do not chase the bubble but slowly move the mirror so the deflections are approximately equal above and below. Paying close attention to where the star is when the sextant is "still" will help you find the perfect alignment. Note that now the assumed elevation on the worksheet remains fixed, and the fine elevation knob is moving only the actual sextant angle, and the position of the star in the field of view. |
| figure 15 Below is a typical night shot, with normal range showing. Generally, the star to be centered will appear brighter than those around it, because you are selecting "bright" stars from the astronomical tables. The real game stars are not used for technical reasons, mainly because they are very faint, and hard to identify in the normal window views. The night view shows no shading or filtering, a "star" smaller than the sun, and other stars in the background. The biggest star is the one to be centered on the now lighted orange bubble ring. The bubble is a bit smaller to match the smaller star. Remember, on the real sextant, the only display is the elevation angle. The distance provided on the worksheet is simply the difference between the assumed and measured elevation angles, where there are 60 nm per degree of difference. If the measured elevation is greater than the assumed elevation, you move the assumed line of position toward the star to plot the true line of position, and vice versa. The figure below is the normal display of the unmagnified view through the eyepiece. This is the "night" display of a bright star, unfiltered, and a lighted bubble. The fine elevation knob controls the sextant mirror, and clicking on the + sign will move the star up in the display (by reducing the mirror angle). What is being simulated is the undulating and cycling of the apparent position of the star through the sextant, caused by movement of the sextant. This sextant movement causes displacement of the bubble, which lags the star jitter due to its inertia. The proper operation is to slowly move the mirror control so the star is centered in the bubble when the star appears at rest. It will then show roughly equal excursions up and down from the center. The excursions are caused by muscle tremor, by airplane vibration, and saw-tooth auto-pilot corrections to hold the plane straight and level. In this figure the star is not centered in the bubble. This amount of vertical offset is about 15 nm of error, so be careful to get the star as centered in the bubble as you can. Left-right errors do not degrade accuracy unless you get outside the white vertical bars. It is normal to do a star shot while sitting on the runway (well, maybe on the run-up pad). This will confirm the calibration of the sextant, and that the bulbs that light the bubble and display are working alright. |
| figure 16 In the figure below, a successful shot has been made, and this is what the display looks like. It says that you should advance your line of position toward the north by -5 NM. It is true North because the azimuth to the star is "0". It also shows that your measured angle is less than the assumed angle, confirming that you want to move your assumed position away from the direction of the star. After noting the information, press the sextant mode button again to reset the sextant to zero for the next shot. Remember that the line you draw on your chart is an east-west line (a latitude line) because your star is to the north. figure 17 |